1. Field of the Invention
This invention relates to feedback systems, and more particularly to apparatuses, systems and methods for estimating and calibrating particulate production from diesel engines.
2. Description of the Related Art
Environmental concerns have motivated the implementation of emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (“EPA”) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. Generally, emission requirements vary according to engine type. Emission tests for compression-ignition or diesel engines typically monitor the release of diesel particulate matter (PM), nitrogen oxides (NOx), and unburned hydrocarbons (HC). A critical emission of gasoline or other stoichiometric engines is carbon monoxide (CO). Catalytic converters have been implemented in exhaust gas after-treatment systems for spark-ignition engines, eliminating many of the pollutants present in exhaust gas, though historically such aftertreatment systems have not been added to diesel engines. However, to remove diesel particulate matter, typically a diesel particulate filter, herein referred to as a filter, must be installed downstream from a catalytic converter or in conjunction with a catalytic converter.
A common filter comprises a porous ceramic matrix with parallel passageways through which exhaust gas passes. Particulate matter accumulates on the surface of the filter, creating a buildup that must eventually be removed to prevent obstruction of the exhaust gas flow. Common forms of particulate matter are ash and soot. Ash, typically a residue of burnt engine oil, is substantially incombustible and builds slowly within the filter. Soot, chiefly composed of carbon, which is refractory and not easily wiped away, can be oxidized and driven off of the filter in a process called regeneration. In most applications soot accumulates much faster than ash, to the extent that an estimate of the rate of soot accumulation is substantially equivalent to an estimate of the rate of total particulate accumulation.
Various conditions, including, but not limited to, engine operating conditions, mileage, driving style, terrain, etc., affect the rate at which the engine produces particulate matter, and the rate at which such matter accumulates within a diesel particulate filter.
For purposes of determining when to initiate regeneration of diesel particulate filters based on the amount of accumulated particulate matter on them, it is beneficial to know how much particulate the engine is producing. A method, apparatus and system for doing so are disclosed in this application's parent application. However, problems can arise when, after the determination has been made, one or more of those factors undergo unseen change: aging of the engine, EGR valve malfunction, turbo or fuel injector changes.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for estimating or predicting particulate output from a diesel engine. A further need exists for calibration of such an apparatus, system, and method.